<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style type="text/css">
        .a{
            width: 0;
            /*border-color: red darkcyan wheat maroon;*/
            /*实现上方三角形*/
            /*border-color: orange transparent transparent transparent;*/
            /*实现左上方三角形*/
            border-color: aqua transparent transparent salmon;
            border-width: 200px;
            border-style: solid;
        }
    </style>
</head>
<body>
<div class="a"></div>
</body>
</html>